🫀Anatomy and Physiology II Unit 3 – Cardiovascular System: Blood Composition

Key Components of Blood

• Consists of plasma, the liquid portion of blood (about 55% of total blood volume)
• Contains formed elements including erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets)
  • Erythrocytes comprise approximately 45% of total blood volume
  • Leukocytes and thrombocytes together make up less than 1% of total blood volume
• Includes various proteins such as albumins, globulins, and fibrinogen dissolved in the plasma
• Transports nutrients (glucose, amino acids, lipids), gases (oxygen, carbon dioxide), and hormones throughout the body
• Helps maintain homeostasis by regulating pH, temperature, and osmotic pressure
• Provides a medium for the immune system to function, with leukocytes and antibodies defending against pathogens
• Enables the coagulation cascade, a complex process involving platelets and clotting factors to prevent blood loss

Functions of Blood

• Transports oxygen from the lungs to tissues and carbon dioxide from tissues back to the lungs for excretion
• Delivers nutrients (glucose, amino acids, fatty acids) from the digestive system to cells throughout the body
• Removes metabolic waste products (urea, creatinine, uric acid) from cells and transports them to the kidneys for excretion
• Regulates body temperature by absorbing and distributing heat evenly
  • Blood vessels can constrict or dilate to conserve or release heat, respectively
• Maintains osmotic balance and pH levels (7.35-7.45) in the body through buffers (bicarbonate, phosphate, proteins)
• Protects against infection and foreign substances through the immune system components (leukocytes, antibodies, complement proteins)
• Enables hemostasis, the cessation of bleeding, through the coagulation cascade involving platelets and clotting factors
• Transports hormones (insulin, thyroid hormones, cortisol) from endocrine glands to target tissues for regulation of various physiological processes

Blood Cell Types and Their Roles

• Erythrocytes (red blood cells) are the most abundant blood cells and primarily transport oxygen
  • Contain hemoglobin, an iron-containing protein that binds to oxygen
  • Lack a nucleus and organelles, allowing more space for hemoglobin and efficient oxygen transport
• Leukocytes (white blood cells) are crucial for the immune system and defend against pathogens and foreign substances
  • Granulocytes (neutrophils, eosinophils, basophils) have granules in their cytoplasm and are involved in inflammation and allergic responses
  • Agranulocytes (lymphocytes, monocytes) lack granules and are involved in specific immune responses and antigen presentation
• Thrombocytes (platelets) are small, disc-shaped cell fragments that play a key role in hemostasis and blood clotting
  • Release chemicals that attract more platelets and clotting factors to the site of injury
  • Form a platelet plug to seal the damaged blood vessel and prevent further blood loss
• Hematopoietic stem cells in the bone marrow give rise to all blood cell types through the process of hematopoiesis
• Erythrocytes, leukocytes, and thrombocytes work together to maintain homeostasis, protect against pathogens, and ensure proper oxygen delivery to tissues

Plasma Composition and Properties

• Plasma is the liquid component of blood, making up about 55% of the total blood volume
• Consists primarily of water (90-92%) and serves as a solvent for various substances
• Contains dissolved proteins (7-8%) such as albumins, globulins, and fibrinogen
  • Albumins help maintain osmotic pressure and transport substances (hormones, fatty acids, bilirubin)
  • Globulins include antibodies (immunoglobulins) that are essential for the immune system
  • Fibrinogen is a key protein involved in the blood clotting process
• Transports nutrients (glucose, amino acids, lipids), electrolytes (sodium, potassium, calcium, chloride), and metabolic waste products
• Helps maintain the pH balance of the body through buffer systems (bicarbonate, phosphate, proteins)
• Contributes to the regulation of body temperature by absorbing and distributing heat
• Provides a medium for the exchange of substances between blood and tissues through capillary walls
• Plasma can be separated from the formed elements by centrifugation, allowing for various clinical applications and tests

Blood Formation (Hematopoiesis)

• Hematopoiesis is the process of blood cell formation that occurs primarily in the bone marrow
• Hematopoietic stem cells (HSCs) give rise to all blood cell types through a series of differentiation steps
  • HSCs are self-renewing and can differentiate into myeloid and lymphoid progenitor cells
• Myeloid progenitor cells develop into erythrocytes, thrombocytes, and myeloid leukocytes (granulocytes, monocytes)
  • Erythropoiesis is the formation of erythrocytes and is regulated by the hormone erythropoietin (EPO)
  • Thrombopoiesis is the formation of thrombocytes and is regulated by the hormone thrombopoietin (TPO)
• Lymphoid progenitor cells develop into lymphocytes (T cells, B cells, natural killer cells)
  • T cells mature in the thymus and are involved in cell-mediated immunity
  • B cells mature in the bone marrow and are responsible for antibody production
• Hematopoiesis is regulated by various growth factors and cytokines that control the proliferation, differentiation, and survival of blood cells
• In adults, hematopoiesis primarily occurs in the red bone marrow of the skull, sternum, ribs, vertebrae, and pelvis
• Extramedullary hematopoiesis can occur in the liver, spleen, and lymph nodes under certain pathological conditions

Blood Groups and Compatibility

• Blood groups are determined by the presence or absence of specific antigens on the surface of erythrocytes
• The ABO blood group system is based on the A and B antigens
  • Blood group A has the A antigen, blood group B has the B antigen, blood group AB has both antigens, and blood group O has neither
  • Individuals with blood group A have anti-B antibodies, those with blood group B have anti-A antibodies, those with blood group O have both anti-A and anti-B antibodies, and those with blood group AB have neither
• The Rh blood group system is based on the presence or absence of the D antigen
  • Rh-positive individuals have the D antigen, while Rh-negative individuals do not
• Blood transfusions must be compatible to avoid adverse reactions
  • ABO compatibility: A can receive from A or O, B can receive from B or O, AB can receive from all types, and O can only receive from O
  • Rh compatibility: Rh-positive individuals can receive Rh-positive or Rh-negative blood, while Rh-negative individuals should only receive Rh-negative blood
• Incompatible transfusions can lead to agglutination (clumping) and hemolysis (rupture) of erythrocytes, causing serious complications
• Pregnant women with Rh-negative blood carrying an Rh-positive fetus may develop Rh incompatibility, which can be prevented by administering Rh immunoglobulin (RhIG)

Common Blood Disorders

• Anemia is a condition characterized by a decreased number of erythrocytes or reduced hemoglobin content
  • Can be caused by blood loss, decreased erythrocyte production (iron deficiency, vitamin B12 deficiency, aplastic anemia), or increased erythrocyte destruction (hemolytic anemia)
  • Symptoms include fatigue, pallor, shortness of breath, and dizziness
• Leukemia is a group of cancers affecting leukocytes, characterized by the uncontrolled proliferation of abnormal white blood cells
  • Can be acute (rapid progression) or chronic (slow progression) and myeloid or lymphoid in origin
  • Treatment options include chemotherapy, radiation therapy, targeted therapy, and stem cell transplantation
• Thrombocytopenia is a condition characterized by a low platelet count, which can lead to increased risk of bleeding
  • Can be caused by decreased platelet production (aplastic anemia, myelodysplastic syndrome), increased platelet destruction (immune thrombocytopenia, thrombotic thrombocytopenic purpura), or platelet sequestration (splenomegaly)
• Hemophilia is a group of inherited bleeding disorders caused by deficiencies in specific clotting factors
  • Hemophilia A (factor VIII deficiency) and hemophilia B (factor IX deficiency) are the most common types
  • Treatment involves replacement of the missing clotting factor through intravenous infusions
• Sickle cell disease is an inherited disorder caused by a mutation in the hemoglobin gene, resulting in abnormally shaped erythrocytes (sickle cells)
  • Sickle cells can obstruct blood vessels, causing pain crises, organ damage, and increased susceptibility to infections
  • Treatment includes pain management, hydration, blood transfusions, and hydroxyurea to reduce the frequency of pain crises

Clinical Applications and Tests

• Complete blood count (CBC) is a common blood test that measures the levels of erythrocytes, leukocytes, and thrombocytes
  • Provides information about anemia, infections, leukemia, and platelet disorders
  • Differential leukocyte count assesses the proportions of different types of leukocytes (neutrophils, lymphocytes, monocytes, eosinophils, basophils)
• Blood typing and crossmatching are essential before blood transfusions to ensure compatibility
  • ABO and Rh typing determine the patient's blood group
  • Crossmatching involves mixing the patient's serum with the donor's erythrocytes to check for any adverse reactions
• Coagulation tests (prothrombin time, activated partial thromboplastin time) evaluate the function of the clotting cascade
  • Useful in diagnosing bleeding disorders and monitoring anticoagulant therapy
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are markers of inflammation
  • Elevated levels can indicate the presence of an inflammatory condition, infection, or malignancy
• Blood culture is used to detect the presence of bacteria or fungi in the blood, helping to diagnose bloodstream infections (sepsis)
• Flow cytometry is a technique that analyzes the characteristics of individual cells, useful in diagnosing and monitoring leukemia and lymphoma
• Genetic tests can identify mutations associated with inherited blood disorders, such as sickle cell disease and hemophilia
• Blood tests are crucial for the diagnosis, monitoring, and treatment of various hematological and systemic disorders, providing valuable insights into a patient's health status